Metamaterials: the Early Years in the USA
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EPJ Appl. Metamat. 2014, 1,5 Ó R.W. Ziolkowski, Published by EDP Sciences, 2014 DOI: 10.1051/epjam/2014004 Available online at: http://epjam.edp-open.org RESEARCH ARTICLE OPEN ACCESS Metamaterials: The early years in the USA Richard W. Ziolkowski* Department of Electrical and Computer Engineering, The University of Arizona, Tucson, AZ, USA Received 11 February 2014 / Accepted 6 May 2014 Abstract – Metamaterials are artificial materials formed by embedding highly subwavelength inclusions in a host medium, which yield homogenized permittivity and permeability values. By design they offer the promise of exotic physics responses not generally available with naturally occurring materials, as well as the ability to tailor their prop- erties to specific applications. The initial years of discovery emphasized confirming many of their exotic properties and exploring their actual potential for science and engineering applications. These seed efforts have born the sweet fruit enjoyed by the current generation of metamaterials scientists and engineers. This review will emphasize the initial investigative forays in the USA that supported and encouraged the development of the metamaterials era and the sub- sequent recognition that they do have significant advantages for practical applications. Key words: Artificial dielectrics, Double negative materials, Epsilon negative materials, Metamaterials, Mu negative materials, Plasmonics. 1 Introduction Workshop to be held in November, 1999. These are the kind of events in which the participants have the chance to influence a Artificial materials have had an enormous impact histori- call-for-proposals (CFP). I quite naturally agreed to participate. cally. Well-known examples include the beautiful 13th century I was invited because of our artificial atom/molecule investiga- stained glass windows in Notre-Dame Cathedral and La Sainte- tions and their applications to radar absorbing materials Chapelle in Paris, their colors originating from plasmonic (RAMs) and smart skins (surfaces that could change their char- effects arising from various metallic inclusions in the glasses. acteristics in response to an interrogating signal) [6–11]. These In the late part of the 19th century, Jagadis Chunder Bose pub- efforts had already led to our studies on how one might use lished his work on the rotation of the plane of polarization by these artificial material models to realize absorbing boundary man-made twisted structures, which were indeed artificial chiral conditions (ABCs) in finite difference time domain (FDTD) structures by today’s definition [1]. Karl Ferdinand Lindman simulations [12–15]. They were ‘‘physical’’ realizations of the studied artificial chiral media formed by a collection of ran- (at the time) revolutionary perfect matched layer (PML) domly-oriented small wire helices in 1914 [2]. In the 1950’s ABCs [16]. and 1960’s, the work of Kock [3], for example, explored artifi- Walser released the general invitation in September 1999 cial dielectric light-weight microwave antenna lenses for satel- stating: ‘‘DARPA is interested in gathering information con- lite applications. To understand the Mercury and Gemini cerning the area of artificially constructed materials, or Meta- spacecraft re-entry communication blackout periods, the ‘‘bed materials, which possess qualitatively new responses that do of nails’’ wire grid medium was introduced in the early not occur in nature’’. This was the first time I had seen the 1960’s to simulate the propagation of waves in plasmas [4]. phrase ‘‘Meta-materials’’. As he did in a later paper [17], Walser Artificial electric and magnetic materials were at the heart of explained at the workshop that the choice of name came from the stealth aircraft programs in the 1980’s and beyond. the desire to achieve material performances ‘‘beyond’’ the lim- Similarly, the resurrected interest in artificial chiral materials itations of conventional composites. The workshop program in the 1980’s and 1990’s (see, e.g., [5]) arose from their poten- consisted of an Applications Section [18] and a Materials tial applications as microwave radar absorbers. Modeling and Processing Section [19]. Drs. Stu Wolf and Bill Ziolkowski at the University of Arizona (UAz) was con- Coblenz of DARPA/DSO (Defense Sciences Office) and tacted in July 1999 by Prof. Rodger M. Walser, University of Dr. Valerie Browning, who was at NRL and coming on board Texas at Austin (UT Austin), about an invitation-only DARPA at DARPA at the time, ran the workshop. The presentations *e-mail: [email protected]; were an interesting mixture of results on electromagnetic band- [email protected] gap structures and complex media. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 R.W. Ziolkowski: EPJ Appl. Metamat. 2014, 1,5 The workshop led to an eventual DARPA MURI (Multi- obtained from electromagnetic band-gap (EBG) structures by a University Research Initiative) CFP (MURI Call for Proposals: MIT-Imperial College team [42]. Topic 33, Electromagnetic Metamaterials) in 2001 whose stated A metasurface at telecom frequencies based on SRRs was objective was: ‘‘To model, synthesize, characterize, and develop reported by the collaborative team from Iowa State University, new synthetic metamaterials which exhibit properties that can Karlsruhe Institute of Technology, and FORTH in Crete [43]. be used in a wide range of applications spanning the electro- This Soukoulis-Wegener-led collaboration has led to numerous magnetic spectrum’’. The winning proposal was entitled ‘‘Scal- contributions to the successful development of optical metama- able and Reconfigurable Electromagnetic Metamaterials and terials [44, 45]. However, this team pointed out earlier that Devices’’; the team consisted of several well-known talents because of kinetic inductance effects, SRR-based unit cells [20]. Dr. Browning later described her new program on Metam- would not reach visible frequencies [46] and suggested an alter- aterials at the DARPA Tech 2002 meeting by saying that [21]: native approach [47]. A University of New Mexico and ‘‘A metamaterial is an engineered composite that exhibits supe- Columbia University team proposed yet a different architecture rior properties not observed in nature or in the constituent mate- [48]. The first demonstration of metamaterials in the visible, rials’’. I believe that it is an interesting historical observation which employed a fishnet structure, was reported in [49]by that the term ‘‘metamaterials’’ was truly introduced into the the ISU-Karlsruhe team. Shalaev reviewed the state-of-the-art community because of a DARPA funding opportunity. in [50] and his Purdue team officially reached visible frequen- cies with their fishnet structure in [51]. The Nanophotonics Group at Purdue with their outstanding fabrication capabilities 2 Initial physics and engineering in the Birck Nanotechnology Center has continued to push proof-of-concept efforts DNG effects further into the visible regime. Shalaev and Boardman organized another OSA focus issue on metamaterials Much of the effort in the early metamaterials period in the published in 2006 [52]. USA, like elsewhere in the world, emphasized investigating and On the West coast, Zhang moved from UCLA to UC proving the exotic physics properties of metamaterials. The first Berkeley in 2004 and established the NSF Nano-Scale Science negative index and then negative refraction investigations and and Engineering Center (NSEC). They have demonstrated and experiments were performed at UC San Diego (UCSD) verified many of the hypenlens and superlens concepts [53–55]. [22–25]. At the same time, the seminal applications paper on They made one of the first examples of a superlattice optical the ‘‘perfect lens’’ concept appeared [26]. Full-wave vector sim- metamaterial [56]. They have demonstrated plasmon lasers at ulations and a detailed analysis of double negative (DNG) me- visible frequencies [57]. In the South, Scalora at the Redstone tamaterials confirmed their negative index properties [27]. One Arsenal in Alabama and his collaborators have considered very important precursor to these experiments was the IEEE numerous aspects of DNG media and subwavelength MTT special issue on electromagnetic periodic structures focusing [58]. [28]. Several notable papers were included that emphasized arti- On the East coast, Engheta at the University of Pennsylva- ficial magnetism. The split ring resonator (SRR) was introduced nia (UPenn) had been involved with complex media for many by an Imperial College-GEC-Marconi team [29]. Structured years. He developed a variety of RAMs based on bi-anisotropic surfaces that act as artificial magnetic conductors (AMCs) were materials [59]. It has been demonstrated by many groups now introduced by UCLA teams: the mushroom surface type [30] that the X-medium he introduced [60] can be designed to exhi- and the frequency selective surface (FSS) type [31, 32]. Given bit DNG properties [61]. He also has introduced and developed the timing on all of these papers in relation to the DARPA the paradigm of Metatronics [62–64] and with Alu`, whose is workshop, they clearly had a significant impact on the outcome now at UT Austin, considered how basic antenna concepts of the above mentioned DARPA MURI CFP. can used successfully to design and analyze nano-antennas